Showing strain (5)
I believe the answer is:
tense
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">showing strain</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for tense that I've seen before include "Anxious - future, perhaps?" , "Future, possibly" , "Verb form, indicates time" , "It may be perfect" , "Strained - form of verb" .)